Athanasiu previously served as Prime Minister on an ad interim basis for 9 days between 13 December and 22 December 1999, heading the Romanian Democratic Convention (CDR) cabinet after the resignation of Radu Vasile (PNȚCD.
An author of several scientific works, he is the recipient of a PhD in Law, as well as a professor at the University of Bucharest (since 1999).
Having joined the newly created PSDR after the Romanian Revolution of 1989, Athanasiu was first elected to Parliament as a deputy in 1992, being nominated to the Committee for Labor and Social Protection.
A Minister of Labor in the Victor Ciorbea CDR cabinet, he retained the office under Radu Vasile and his own premiership, being replaced by Smaranda Dobrescu during the leadership of Mugur Isărescu.
In 2003–2004, Athanasiu also served as Minister of Education in the Adrian Năstase executive (replacing Ecaterina Andronescu).